The present invention generally relates to electrostatic filters. More particularly, the invention relates to the use of insulated electrodes in electrostatic filters.
There are currently a wide range of technologies that are used to purify and/or filter air. One such technology is the electrostatic filter. Generally electrostatic filters include a porous dielectric material that is positioned between a pair of electrodes. A fluid stream (e.g., air) is arranged to pass through the dielectric material. In an active electrostatic filter, a significant potential difference is applied across the electrodes in order to induce an electrostatic field in the dielectric material that is sufficient to cause particulates within the air stream passing through the filter to adhere to the dielectric.
More recently, ion enhanced electrostatic filters have been developed. An ion enhanced electrostatic filter contemplates placing an ion source in front of the electrostatic filter to impart an electric charge to some of the particulates carried by air passing through the filter. The charges imparted to the particulates by the ionizer tend to help their collection within the dielectric.
U.S. Pat. No. 5,474,600, which is owned by the assignee of the present application, discloses an apparatus for the biological purification and filtration of air. Generally, the '600 patent discloses a system which utilizes a course electrostatic filter 1, a cylindrical or polygonal ionizer 5 and a fine electrostatic filter 10 that are all arranged in series. In some of the described embodiments, a pair of ionizers that impart opposite charges are arranged in series between the course and fine electrostatic filters. The system is arranged to inactivate (i.e. kill) biological objects (e.g., microorganisms and viruses) that are carried in the air stream and to filter particulates from the stream.
Commercial embodiments of this type of air purification and filtration system have been successfully used in the MIR space station and in hospitals to purify, filter and decontaminate air. A representative commercial embodiment of such a system is diagrammatically illustrated in FIG. 1. As seen therein, the system 20 include an electrostatic pre-filter 22, a positive plasma generator 24 that is arranged in series with a negative plasma generator 26 and a series of four electrostatic filters 28 that are arranged downstream of the negative plasma generator 26. Each D.C. plasma generator 24, 26 is composed of a plurality of cylindrical plasma cylinders (e.g., 6 cells) arranged in parallel. Each cell has a needle type ionizing electrode that is surrounded by a cylindrical electrode chamber. One of the electrodes is grounded while a D.C. potential of either 4000 or 7600 volts is applied to the opposing electrode. The electrostatic filters may be formed as described in U.S. Pat. Nos. 5,474,600 or 6,805,732 and plasma generator may be formed as described in U.S. Pat. No. 5,474,600 or U.S. Published Application No. 2005/0098040. All of these patents and patent applications are incorporated herein by reference.
Although the described system works well, there are continuing efforts to provide improved and/or more cost effective purification and/or filtering devices that can meet the needs of various applications.